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PubMed1992

[Elemental analytical and quantitative morphometric determination of the synthetic resin residues and enamel avulsion after the removal of metal brackets].

A number of clinical and experimental studies were performed to assess the quality of the enamel-adhesive-bracket bond. The aim was to present a combined method that enables the investigator both to examine the surface of metal brackets quantitative-morphometrically and to detect the presence of enamel particles. To this end, 38 metal brackets were examined in the scanning electron microscope. An EDAX-detecting unit was used to analyze morphologically conspicuous structures and identified them as enamel particles. The extent of adhesive remnants and enamel particles was quantified using the image analysis system IBAS. In 24 brackets (53%) bonding adhesive residue was found on the bracket base. In 18 brackets (47%) enamel particles were identified on the adhesive-bearing brackets. This method is easier to carry out and enables a more accurate quantification of enamel particles than the Adhesive Remnant Index. Since it can be applied universally to examine recommended improvements to adhesive technique, it facilitates their assessment.

Composite Resins↗
PubMed1983

Ca-enriched amorphous mineral deposits associated with the plasma membranes of chondrocytes and matrix vesicles of rat epiphyseal cartilage.

Electron microscopic study of tibial epiphyseal plates of young growing rats revealed amorphous-appearing electron dense deposits 5-35 nm in diameter, associated with the plasma membranes of more than 43% of the proliferative zone chondrocytes. Hypertrophic zone chondrocytes, however, revealed no plasma membrane-associated amorphous-appearing deposits. The membrane-associated densities were observable in unstained sections of tissues fixed in glutaraldehyde alone and in tissues double-fixed with glutaraldehyde and osmium tetroxide, and were extracted from ultrathin sections floated on neutral aqueous solutions of 4% ethyleneglycol bis-(beta-aminoethyl ether) N,N'-tetraacetic acid (EGTA) for one-half hour. Energy dispersive X-ray analysis of the densities in scanning transmission electron microscope (STEM) mode revealed the presence of Ca, suggesting that the membrane-associated amorphous-appearing deposits are Ca-enriched. Similar deposits were observed in the membrane of matrix vesicles present in the longitudinal cartilaginous septae in the hypertrophic zone. Four types of matrix vesicles were encountered in the longitudinal cartilaginous septae; one type with amorphous-appearing deposits, another with crystallites, a third type with both amorphous-appearing and crystalline-like deposits, and a fourth that is empty. These observations are interpreted to indicate that chondrocytes of the reserve and proliferative zones play a direct role in mineralization by elaborating amorphous mineral deposits along their plasma membranes. These deposits are incorporated into budding matrix vesicles, which then play a role in the initiation of mineralization by supporting the spontaneous phase transformation of amorphous-appearing mineral to crystalline mineral.

Animals↗
PubMed1983

The fine structure of pancreatic stones as shown by scanning electron microscopy and X-ray probe microanalyser.

To delineate the process of pancreatic stone formation, stones from four patients were studied with a scanning electron microscope and X-ray probe microanalyser. The stones consisted of a central core and surrounding shell. Two kinds of stones were demonstrated: one had a core composed of a calcium-rich amorphous substance and interlacing fibrils; the other had a core consisting of multiple cavities with smooth walls composed of a calcium-deficient amorphous substance. The shells showed a common structure: zones of layers or bands of a calcium-rich amorphous substance, network fibrils filled with a calcium-rich amorphous substance, and laminated parallelogrammic or polygonal plates of calcite parallel to the surface in one layer and oblique or perpendicular in the next layer. Calcium was in the crypto-crystalline state as well as crystalline state of calcite. Crystalline calcite showed spiral and epitaxial growth along with findings of dissolution, resembling cholesterol crystals of gall stones. Pancreatic stones are probably formed through central core formation and layered growth of a shell. Comparison of stones and protein plugs suggests that protein plugs can grow to stones with calcite deposition accompanied by precipitation of network fibrils and an amorphous substance.

Bacteria↗
PubMed2003

The influence of fluoride exposure on dentin mineralization using an in vitro organ culture model.

This study aimed to characterize fluoride-induced alterations in dentin mineralization within a dentin-pulp organ culture system. Tooth sections derived from male Wistar rat incisors were cultured in Trowel-type culture for 14 days, in the presence of 0 mM, 1 mM, 3 mM and 6 mM sodium fluoride. Tooth sections were processed and analyzed for uptake of fluoride, its subsequent effect on dentin mineralization by tetracycline hydrochloride incorporation and mineral composition, expressed as calcium/phosphorous (Ca/P) ratios. Tetracycline hydrochloride incorporation was demonstrated to decrease with increased fluoride exposure, accompanied by significant increases in both Ca/P ratios and fluoride incorporation. These findings provide further evidence that the established alterations in dentin formation during fluorosis are a consequence of disruption to the mineralization process, and provide a model system with which to investigate further the potential role the extracellular matrix plays in inducing the apparent changes in mineral composition.

Animals↗
PubMed2007

Mechanism of calcium accumulation in acetate-fed aerobic granule.

High calcium content has been widely reported in acetate-fed aerobic granules, but the reason behind this is unclear yet. By SEM-energy dispersive X-ray mapping analysis, this study showed that the majority of calcium was presented in the central part of the acetate-fed aerobic granule, and the granule shell part was nearly calcium-free. The elemental analysis of calcium ions coupled with the chemical titration of carbonate further revealed that the calcium ions that accumulated in the acetate-fed aerobic granule mainly existed in the form of calcium carbonate (CaCO3). The formation of the CaCO3 appeared to be highly dependent on the size of the aerobic granule, i.e., the CaCO3 precipitation was found only in aerobic granules with radiuses larger than 0.5 mm. These experimental observations with regard to the formation of CaCO3 in the acetate-fed aerobic granule were further confirmed by the model simulation, which was based on the principles of mass diffusion and carbonate dissociation in liquid phase. This study for the first time showed that the size of the acetate-fed aerobic granule would indeed play an essential role in the CaCO3 formation, and provided experimental evidence that a crystal CaCO3 core was not necessarily required for granulation.

Acetates↗
PubMed1999

Investigation of different ontogenetic stages of Raillietiella sp. (Pentastomida: Cephalobaenida): excretory functions of the midgut.

The midgut of Raillietiella sp. was investigated in different ontogenetic stages. The developing embryo, the hatched first-stage larva, the infective fourth-stage larva from the intermediate host, and juveniles and adults from the definitive host were viewed ultrastructurally. From the fourth-stage larva onward, spherocrystals were visible in the midgut cells. They contained only small amounts of calcium and iron, depending on the ontogenetic stage. The cycle of crystal formation and destruction or excretion, respectively, is described herein. Their role in ion regulation and excretion is discussed with regard to similar inclusions in other arthropods.

Animals↗
PubMed2005

Application of cryofixation and cryoultramicrotomy for biological electron microscopy.

Conventional chemical fixation and embedding of specimens in resins are accompanied by many artifacts, including postmortem structural alterations. Antigenicity of constituents of specimens can be deteriorated and soluble elements relocated in the process of chemical fixation and resin-embedding. Cryofixation and cryoultramicrotomy will overcome many of these drawbacks of chemical fixation and resin embedding. The theoretical background, equipment, methods, and applications of cryofixation and cryoultramicrotomy for biological specimens are reviewed.

Cryopreservation↗
PubMed1982

Corrosion of resin-bonded orthodontic brackets.

The objective was to identify the nature and origin of indelible black and green stains found in enamel after the removal of bonded orthodontic brackets. Several brackets were examined by scanning electron microscopy and energy-dispersive x-ray analysis. Irrespective of the type of bracket or resin, morphologic evidence of corrosion activity was found. Brackets were pitted, and in some cases large amounts of metal were missing. Cracks were found in the resin which led to sites of destruction in which structures resembling microorganisms were also found. X-ray analysis showed the presence of chromium, nickel, iron, and chlorine in significant amounts in the bonding, discolored resin. It was concluded that the cracks were favoring crevice corrosion. In the presence of organisms and a lowered pH, together with a chloride environment and an oxygen gradient, conditions conducive to corrosion are established.

Chemical Phenomena↗
PubMed1992

Physical examination of caffeine's effects on the enamel surface of first molar in new-born rats.

Samples of the first molars of offspring whose dams were fed a diet supplemented with caffeine were examined by scanning electron microscopy, X-ray diffractometry and electron microprobe analysis. Scanning microscopy of the enamel surface of the caffeine group revealed a consistently rougher surface than in the non-caffeine controls, both before and after acid exposure. X-ray diffraction analysis of the pulverized whole tooth in the caffeine group showed broader diffraction peaks for the lattice plane reflections (202) and (300), indicating smaller crystallites. Pure enamel samples of the caffeine group examined with a Gandolfi X-ray camera also revealed more diffuse diffraction lines than in the non-caffeine controls, further indicating smaller crystallites in the enamel. The calcium and phosphorus contents of the acid-exposed samples in both control and caffeine groups were lower than the non-acid exposed control and caffeine groups by electron microprobe analysis. After exposure to acid, the calcium and phosphorus contents of the outer surface of the enamel in the caffeine group were greatly reduced as compared to that of the non-caffeine controls. Thus various methods consistently indicate that caffeine ingestion during early growth affects the enamel surface of the first molars, resulting in impaired mineralization. Caffeine intake may therefore have a negative effect on amelogenesis and possibly increases susceptibility to dental caries.

Animals↗
PubMed1995

Distribution of moderately volatile trace elements in fine-grained chondrule rims in the unequilibrated CO3 chondrite, ALH A77307.

The concentrations of Ni, Cu, Zn, Ga, Ge, and Se in five, fine-grained chondrule rims in the highly unequilibrated CO3 chondrite ALH A77307 (3.0) have been determined for the first time by synchrotron X-ray fluorescence (SXRF) microprobe at Brookhaven National Laboratory. These elements are especially useful for tracing the role of condensation and evaporation processes which occurred at moderate temperatures in the solar nebula. Understanding the distribution of moderately volatile elements between matrix and chondrules is extremely important for evaluating the different models for the volatile depletions in chondritic meteorites. The data show that the trace element chemistry of rims on different chondrules is remarkably similar, consistent with data obtained for the major and minor elements by electron microprobe. These results support the idea that rims are not genetically related to individual chondrules, but all sampled the same reservoir of homogeneously mixed dust. Of the trace elements analyzed, Zn and Ga show depletions relative to CI chondrite values, but in comparison with bulk CO chondrites all the elements are enriched by approximately 1.5 to 3.5 x CO. The abundance patterns for moderately volatile elements in ALH A77307 chondrule rims closely mimic those observed in the bulk chondrite, indicating that matrix is the major reservoir for these elements. The close matching of the patterns for the volatile depleted bulk chondrite and enriched matrix is especially striking for Na, which is anomalously depleted in ALH A77307 in comparison with average CO chondrite abundances. The depletion in Na is probably attributable to the effects of leaching in Antarctica. With the exception of Na, the volatile elements show a relatively smooth decrease in abundance as a function of condensation temperature, indicating that their behavior is largely controlled by their volatility.

Electron Probe Microanalysis↗
PubMed1982

Quantitative SEM analysis of injury to the endothelium of rabbit aorta and carotid artery during experimental atherosclerosis.

The luminal surface of the aorta and the carotid artery in normal and cholesterol-fed rabbits (3 weeks, 6 weeks, and 8 months of alimentary hypercholesterolemia) was studied by scanning electron microscopy (SEM). To study endothelial injury the vessels were perfused and stained under physiological pressure. The frequency of large and small endothelial defects was determined per surface unit of endothelium in the normal and experimental groups of rabbits. Loss of endothelial cells was regarded as a large defect, argyrophilic cells, craters, and stomata were regarded as small ones. It was found that the percentage of regions without endothelial cells was similar in both control rabbits and in rabbits with experimental atherosclerosis (0.005--0.04% of the total surface examined). The frequency of small endothelial defects increased in rabbits after 3 weeks of hypercholesterolemia but decreased to the control level after 6 weeks of hypercholesterolemia. In rabbits with 8 months of hypercholesterolemia the frequency and area of defects outside plaques did not differ from the control group. In the group with hypercholesterolemia for 8 months 39.2% of the plaque surface contained endothelial cells in which there were no distinct silver-stained cell borders. Kevex X-ray spectrometric data of silver topography indicated that the plaque surface without distinct cell borders was not an area devoid of cells. The data obtained do not support the assumption that morphological endothelial injury is the structural precursor of plaque formation.

Animals↗
PubMed1984

Phosphocitrate and its analogue N-sulpho-2-amino tricarballylate inhibit aortic calcification.

This study reports the ability of phosphocitrate and its enzyme-resistant analogue N-sulpho-2-amino tricarballylate to inhibit aortic calcification. Dystrophic calcification of aorta was induced by transplanting fresh aortic segments in Millipore chambers to the peritoneal walls of recipient rats. Daily intraperitoneal injection of the new inhibitors remarkably reduced calcium accumulation by the aortae and prevented the appearance of hydroxyapatite-like crystalline structures. Phosphocitrate was the most effective of the anti-calcifying agents tested, preventing aortic calcification at 1 mumole/day/rat. N-sulpho-2-amino tricarballylate was less effective, reducing aortic calcification by 60% at 10 mumoles/day/rat. The new inhibitors might prove therapeutically useful in man to arrest soft tissue calcification.

Animals↗
PubMed1980

Light microscopy, scanning electron microscopy, and microprobe analysis of bone response to zinc and nonzinc amalgam implants.

Freshly mixed, unset zinc-free and zinc-containing analgam was implanted in the right tibia of 32 rats. Half of the specimens were examined by the light microscope and the other half by the scanning electron microscope and x-ray microprobe analysis. It was found that amalgam is well tolerated by the rat osseous tissue, and there were no histologic reaction differences between zinc and zinc free amalgam. The surfaces of the implants were covered by an organic film at 3 weeks and with bone at later intervals. Very little corrosion products containing sulfur were observed on the amalgam surface at all intervals. Bone adjacent to the amalgam contained tin and sulfur irrespective of the presence of zinc in the alloy, indicating outward migration of specific components of the alloy.

Animals↗
PubMed1991

Characterization of the enamel ultrastructure and mineral content in hypoplastic amelogenesis imperfecta.

Amelogenesis imperfecta (AI) comprises a diverse group of hereditary enamel disorders that are characterized by hypoplastic and in some cases hypomineralized defects. The specific biochemical abnormalities remain unknown for all AI types, making histologic and chemical analyses of affected dentitions essential for resolving the etiology of AI. The purpose of this investigation was to characterize the ultrastructure and mineral content of smooth hypoplastic AI enamel. The AI enamel showed no evidence of surface pitting and was uniformly reduced in thickness by approximately 60% compared with control enamel. Imbibition studies indicated that the AI enamel was generally porous. The first 30 microns of AI enamel adjacent to the dentinoenamel junction was translucent with poorly formed prisms. Abnormal prism structure was seen throughout the AI enamel. Amorphous, presumably organic material that may have been retained enamel protein was also seen. Although the crystallite widths were similar in both AI and normal enamel, the AI teeth showed areas where the crystallite order and continuity appeared disrupted. The mean mineral content was similar for all variables measured except sodium, which was significantly lower in the AI teeth. The calcium concentration was very low in the AI enamel directly adjacent to the dentinoenamel junction and showed a steeper concentration gradient moving from the dentin to the surface compared with control teeth. It may be concluded that the ameloblasts in smooth hypoplastic AI produce a tissue of reduced thickness, which is excessively porous and displays alterations in its ultrastructural organization.

Ameloblasts↗
PubMed1988

Effects of stimulation on the ultrastructure and Na, K, Cl composition of the fundus of the rat plantar sweat gland.

Initial stimulation of the rat plantar sweat gland with pilocarpine caused a variable degree of distension of the apical membrane of the secretory cell. This appeared to be a process of filtration of secretory cell cytoplasm through the apical terminal web. Further stimulation resulted in luminal dilatation, cytoplasmic depletion, and morbidity of some cells. These morphological changes in the footpad gland, which thus can no longer be considered as eccrine, were accompanied by a fall in potassium and a rise in sodium concentration within the secretory cells. The mode of secretion induced by pharmacological stimulation was fundamentally the same as that in the glands of species responsive to thermal stimulation.

Animals↗
PubMed1993

Auger electron spectroscopy of dentin: elemental quantification and the effects of electron and ion bombardment.

Auger electron spectroscopy was used in this investigation to quantify the elemental composition of various dentin surfaces. The surfaces included the "smeared layer," produced by abrasion, as well as surfaces prepared by fracturing in vacuum and in air. Quantification was aided by spectra obtained from standard samples of the two main components of dentin, hydroxyapatite, and collagen. Experimental conditions were found whereby the samples could be analyzed without conductive coatings. Ion sputter etch rates were measured for dentin, hydroxyapatite, and collagen. Under the conditions used here, it was observed that collagen etched at a rate approximately five times greater than hydroxyapatite. Auger spectra of the sputtered surfaces indicated significant ion beam-induced sample changes in collagen and dentin; no significant changes were found with hydroxyapatite. The results of this investigation demonstrate that Auger electron spectroscopy can be used to characterize dentinal surfaces and that ion sputtering can cause changes in the surface composition of dentin.

Collagen↗